1. Field
An embodiment relates to a pixel and an organic light emitting display device including the pixel.
2. Description of Related Art
Recently, a variety of flat panel displays that makes it possible to reduce the weight and the volume in comparison to cathode ray tubes, have been developed. Typical flat panel displays include liquid crystal displays, field emission displays, plasma display panels, and organic light emitting display devices, etc.
The organic light emitting display device displays an image, using organic light emitting diodes that produce light by recombining electrons and holes. The organic light emitting display device has high response speed and is driven with low power consumption.
FIG. 1 is a circuit diagram illustrating a pixel of an organic light emitting display device in the related art.
Referring to FIG. 1, a pixel 4 of an organic light emitting display device of the related art includes: an organic light emitting diode OLED; and a pixel circuit 2 connected with a data line Dm and a scan line Sn and controlling the organic light emitting diode OLED.
The anode electrode of the organic light emitting diode OLED is connected to the pixel circuit 2 and the cathode electrode is connected to the second power supply ELVSS. The organic light emitting diode produces light with predetermined luminance in response to the current supplied from the pixel circuit 2.
The pixel circuit 2 controls the amount of current supplied to the organic light emitting diode OLED, in response to a data signal supplied to the data line Dm, when a scan signal is supplied to the scan line Sn. For this configuration, the pixel circuit 2 includes: a second transistor M2 connected between a first power supply ELVDD and the organic light emitting diode OLED; a first transistor M1 coupled to the second transistor M2, the data line Dm, and the scan line Sn; and a storage capacitor Cst connected between a gate electrode and a first electrode of the second transistor M2.
A gate electrode of the first transistor M1 is connected to the scan line Sn and a first electrode of the first transistor M1 is connected to the data line Dm. Further, a second electrode of the first transistor M1 is connected to one terminal of the storage capacitor Cst. In this configuration, the first electrode is one of a source electrode and a drain electrode and the second electrode is the other electrode different from the first electrode. For example, when the first electrode is the source electrode, the second electrode is the drain electrode. The first transistor M1 connected to the scan line Sn and the data line Dm is turned on and supplies a data signal, which is supplied through the data line Dm, to the storage capacitor Cst. In this operation, the storage capacitor Cst is charged with a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is connected to one terminal of the storage capacitor Cst and the first electrode of the second transistor M2 is connected to the first power supply ELVDD and the other terminal of the storage capacitor Cst. Further, the second electrode of the second transistor M2 is connected to the anode of the organic light emitting diode OLED. The second transistor M2 controls the amount of current flowing from the first power supply ELVDD to the second power supply ELVSS through the organic light emitting diode OLED, in accordance with the voltage value stored in the storage capacitor Cst. In this configuration, the organic light emitting diode OLED emits light corresponding to the amount of current supplied from the second transistor M2.
However, the pixel 4 of the organic light emitting display device of the related art may not display an image with uniform luminance. To be more specific, the second transistors M2 (i.e., driving transistor) in the pixels 4 have different threshold voltages for each pixel 4 due to process variation during manufacturing. As the threshold voltages of the driving transistors are different, light with different luminance is generated by the difference in the threshold voltage of the driving transistors, even if data signals corresponding to the same gradation are supplied to the pixels 4.
In order to overcome the problems, a structure additionally forming a transistor in each pixel 4 to compensate for the threshold voltage of the driving transistor has been disclosed. Practically, a structure using six transistors and one capacitor for each pixel 4 to compensate for the threshold voltage of a driving transistor has been disclosed (Korean Patent Publication No. 2007-0083072). However, the six transistors included in the pixel 4 complicate the pixel 4. In particular, the possibility of malfunction is increased and yield is correspondingly decreased by the transistors in the pixels.